Perioperative quality indicators among neurosurgery patients: A retrospective cohort study of 1142 cases at a tertiary center

Objective The purpose of this study was to present the first comprehensive analysis of perioperative quality indicators; length of hospital stay; readmission; reoperation; pre-, intra, and postoperative events; and mortality in a diverse neurosurgical patient cohort in Europe. Methods Electronic medical records of all patients who were admitted to our institution between January 1 and December 31 of 2020, and underwent an index neurosurgical operation (n = 1142) were retrospectively reviewed. Results The median length of hospital stay at the index admission and readmission was 8 days (range: 1–242 days) and 5 days (range: 0–94 days), respectively. Of the 1142 patients, 22.9% (n = 262) had an extended length of hospital stay of ≥14 days. The all-cause 7-, 15-, 30-, 60-, and 90-day readmission rates were 3.9% (n = 44), 5.7% (n = 65), 8.8% (n = 100), 12.3% (n = 141), and 16.5% (n = 188), respectively. The main reason for unplanned readmission was deterioration of medical and/or neurological condition. The all-cause 7-, 15-, 30-, 60-, and 90-day reoperation rates were 11.1% (n = 127), 13.8% (n = 158), 16.5% (n = 189), 18.7% (n = 213), and 19.4% (n = 221), respectively. Unplanned reoperations were due primarily to hydrocephalus. The rate of preoperative events was 1.1% (n = 13), one-third of which were associated with infection. The rate of intraoperative events was 11.0% (n = 126), of which 98 (64.47%) were surgical, 37 (24.34%) were anesthesiologic, and 17 (11.18%) were associated with technical equipment. The rate of postoperative events was 9.5% (n = 109). The most common postoperative event was malfunction, disconnection, or dislocation of an implanted device (n = 24, 17.91%). The mortality rates within 7, 15, 30, 60, and 90 days after the index operation were 0.9% (n = 10), 1.8% (n = 21), 2.5% (n = 29), 3.4% (n = 39), and 4.7% (n = 54), respectively. Several patient characteristics and perioperative factors were significantly associated with outcome parameters. Conclusions This study provides an in-depth analysis of quality indicators in neurosurgery, highlighting a variety of inherent and modifiable factors influencing patient outcomes.


Introduction
In recent years, growing emphasis has been placed on value-based healthcare rather than volume-based healthcare.Advancing the efficiency of healthcare delivery by improving patient outcomes relative to costs not only benefits patients but also increases the economic sustainability of healthcare systems [1].Accordingly, parameters assessing patient outcomes, such as the length of hospital stay (LOS), readmission rate, reoperation rate, adverse event rate, and mortality rate, are increasingly used as quality metrics [2][3][4][5][6][7][8].
The average LOS varies greatly among countries and healthcare systems, and this variation cannot be explained by medical reasons or necessity [9,10].As reported by the Organisation for Economic Co-operation and Development, the average LOS in Austria is longer than that in Anglo-American and Scandinavian countries, but shorter than that in Germany [11].Decreasing the LOS in German-speaking countries is important, because research has suggested that each day spent in the hospital confers additional risks on patients regardless of their primary diagnoses [12].Hospital-acquired conditions such as air embolism, blood incompatibility, catheter-associated infections, poor glycemic control, and surgical site infections continue to markedly threaten patient safety [13].
Hospital readmission rates can indicate substandard care and unfavorable patient outcomes [4,14,15].As a quality parameter, they indicate the effect of hospital care on patient condition after discharge [16].Rehospitalization occurs frequently and may continue to be life-threatening [17].Because inpatient acute care is the most expensive type of health service, hospital readmission results in substantial healthcare costs [16].Research has suggested that a sizable proportion of readmissions may potentially be avoidable [14].
Reoperation rates are increasing being used as another quality indicator, because of their wide applicability and straightforward determination [18].According to a study in five European hospitals, 1 minute of operating room time costs approximately 9.45 € in a conventional surgical theater [19].In hybrid operating rooms, which are also frequently used for neurosurgical procedures, the average cost is more than twice as high, at 19.88 € [19].Given that neurosurgical operations generally have longer durations than operations in other specialties, unplanned returns to the operating room can greatly increase the overall costs of patient care [20].
Adverse events after neurosurgical procedures are not rare [7].These events not only endanger patients' health status, but are also associated with extended LOS, readmission, and reoperation, thereby resulting in substantial healthcare costs [5,7,21].The incidence of adverse events after surgical operations is expected to rise even further, as a consequence of aging of the population and increased burden of illness worldwide [21].In previous studies, prolonged length of preoperative hospital stay has been identified as a modifiable risk factor for various postoperative adverse events [22][23][24][25].However, an overview of in-hospital complications between hospital admission and index operation is currently not available.Moreover, the overall incidence rate of intraoperative complications among neurosurgery patients has not been investigated in the literature to date.Earlier work in this area was either procedure specific or focused on only pediatric patients.Moreover, no report to date has described the predictive factors associated with intraoperative complications in neurosurgery [26][27][28][29][30].
Therefore, the aim of this study was to present what is, to our knowledge, the first analysis of perioperative quality indicators in a diverse neurosurgical patient cohort in a European healthcare system.

Design and setting
This study was a retrospective cohort analysis of patients at the Department of Neurosurgery of the Vienna General Hospital, Medical University of Vienna.Approval was granted by the ethics committee of the Medical University of Vienna (number 1360/2021), in accordance with the issued Guidelines for Good Scientific Practice.The requirement for informed patient consent was waived by the ethics committee.The Vienna General Hospital is a tertiary referral center, and the largest hospital in Austria and fifth largest hospital in Europe.It has a capacity of 1732 beds [31], and more than 61000 inpatient admissions and more than 1.1 million outpatient visits per year [32].
Electronic medical records of all patients (n = 1142) who were admitted to our institution between January 1 and December 31 of 2020, and underwent an index neurosurgical operation were retrospectively reviewed.Data collection was performed through the patient information management system (AKIM) of Vienna General Hospital by the first author between June 1, 2021, and July 20, 2022.Only the first author had access to information that could be used to identify individual participants during or after data collection.

Outcome variables
The primary outcome measures of interest were the LOS at the index admission and readmission; rates of all-cause and unplanned readmission within 7, 15, 30, 60, and 90 days after discharge from the index admission; causes of readmission; International Classification of Diseases 10th Version (ICD-10) diagnosis codes at readmission; rates of all-cause and unplanned reoperation within 7, 15, 30, 60, and 90 days after the index operation; ICD-10 diagnosis codes at reoperation; procedures performed at reoperation; causes of reoperation; pre-, intra-, and postoperative events and their rates; time until adverse events; and mortality rates within 7, 15, 30, 60, and 90 days after the index operation.

Definitions of outcomes
In this study, the LOS spanned from hospital admission to discharge.Extended LOS was defined as a hospital stay exceeding the 75th percentile for the overall cohort (�14 days).Index hospital admission refers to the first hospital admission of patients to the Department of Neurosurgery of the Vienna General Hospital, in which neurosurgical operation was performed.The index operation was defined as the first neurosurgical operation performed at the Department of Neurosurgery of the Vienna General Hospital.Readmission refers to return to the Vienna General Hospital for any cause after prior discharge.Reoperation describes a repeat neurosurgical procedure after the index surgery.Preoperative events were defined as any adverse event that occurred in the hospital between the index admission and the index operation.Intraoperative events describe any adverse events occurring in the operating theater during the index surgery, as described by the operating surgeon.Postoperative events were defined as any abnormal or unexpected neurosurgical events occurring within 90 days after the index surgery, and contributing to prolonged hospitalization, readmission, or reoperation.Detailed definitions of postoperative events are provided in Table 10 in the S1 Appendix.

Statistical analysis
SPSS1 statistics software, version 29 (IBM Corporation), was used for statistical analysis.Descriptive statistics, including means, medians, rates, ranges, percentages, and standard deviations, was used to describe the collected patient datasets.Univariate analyses between categorical variables were performed with Pearson's χ2 test, Fisher's exact test, the Fisher-Freeman-Halton exact test, or logistic regression, as appropriate.A Monte Carlo simulation was applied, if necessary, with a confidence level of 99% and 10000 samples.Continuous variables were compared via Mann-Whitney U test or independent-samples Kruskal-Wallis test with Dunn-Bonferroni post hoc analysis.Multivariate logistic regression models were built with an entry criterion of p<0.05 to further investigate the independent predictors of extended LOS, unplanned readmission, unplanned reoperation, perioperative events, and mortality.The Hosmer-Lemeshow test was used to determine the calibration of the models.A p-value less than 0.05 was defined as statistically significant.All reported p-values are two-sided.

Results
The baseline characteristics of the 1142 patients in the study population are presented in Table 1.The evaluated operative metrics and their outcomes are summarized in Table 2.The preoperative laboratory values of the patients and their outcomes are shown in Table 1 in the S1 Appendix.The assessments of additional patient characteristics and clinical parameters are reported in Table 2 in the S1 Appendix.A subgroup analysis of pediatric patients in various age groups is shown in Table 3 in the S1 Appendix.

Length of hospital stay
The overall LOS of the entire patient cohort at the index hospitalization ranged from a 1 to 242 days.On average, the patients spent a median of 8 days at the hospital during the index admission.The median LOS until the index operation was 1 day (range: 0-50 days), whereas the median LOS after the index operation was 7 days (range: 0-242 days).Patients with an          extended LOS remained in the hospital for a median of 21.5 days (range: 14-242 days).In contrast, patients without prolonged hospitalization stayed in the hospital for a median of 7 days (range: 1-13 days).The cohort of patients with hydrocephalus had the longest median LOS (median 14 days, range 3-111 days), whereas the shortest median LOS was observed among patients undergoing spinal neurosurgery (median 6 days, range 1-74 days) (Table 1).The median length of the index hospitalization for the most frequent tumor histologies was 9 days for meningioma (range: 3-127 days), 13 days for glioblastoma (range: 2-87 days), 9 days for vestibular schwannoma (5-53 days), 8 days for pituitary adenoma (range: 5-30 days), and 10 days for pilocytic astrocytoma (range: 6-21 days).Patients with WHO grade I, II, or III tumors spent a median of 9 days in the hospital during the index stay, whereas patients with WHO grade IV tumors remained in the hospital for a median of 13 days.

Perioperative events
In the study cohort, 13 patients experienced a total of 15 preoperative events.The overall rate of preoperative events was 1.1%.The duration until the preoperative events was known in 8 of 15 cases, and amounted to a median of 0 days (range: 0-11 days).Approximately three-quarters of the preoperative events occurred in the general ward (n = 11, 73.33%), whereas the rest were reported during intensive care unit or intermediate care unit stays (n = 4, 26.67%).The rate of intraoperative events in the patient cohort was 11% (n = 126).The total number of intraoperative events was 152.Of these, 98 (64.47%) were surgical, 37 (24.34%) were anesthesiologic, and 17 (11.18%)were technical equipment-related complications (Table 9 in the S1 Appendix).No patients died in the operating theater.The rate of postoperative events was 9.5% (n = 109).The most common postoperative events after elective procedures were pituitary surgery associated events (n = 14) and wound complications (n = 13), whereas the malfunction, disconnection, or dislocation of an implanted device was the most frequently described event after non-elective procedures (n = 13) (Table 11 in the S1 Appendix).A timeto-event analysis indicating the average time until the occurrence of postoperative events is shown in Fig 2 .All events requiring immediate attention, such as hemorrhage or infarcts, occurred within 4 days after surgery.Factors significantly associated with perioperative events in multivariate logistic regression models are summarized in Table 12 in the S1 Appendix.

Discussion
Regular measurement and analysis of outcome parameters is crucial in evaluating the quality of healthcare systems and enabling necessary steps toward improvement.
In our study, the median LOS at the index hospitalization was 8 days, which was longer than the reported neurosurgical hospitalizations in Anglo-American countries [33,34].Approximately one-fifth of patients had an extended LOS of at least 14 days.Our findings highlighted that, despite an observed slow decline in LOS in the nine neurosurgical departments in Austria over the past two decades [35], further initiatives are necessary to avoid hospital days beyond medical readiness [36].
The main reason for the discrepancy in the LOS between European countries such as Austria and countries such as the United States of America lies in historically deep-seated cultural differences regarding when patient discharge is considered safe by physicians and patients, in the absence of any data supporting that longer hospital stays increase safety.Acquiring evidence-based data is the only way to change the perceptions and traditions that have resulted in patients remaining in hospitals until their stiches have been removed, as reflected by the median hospital stay of 8 days.Our study provides evidence that patients without identified risk factors-most importantly neurological compromise, diminished albumin, elevated prothrombin time at admission, and intraoperative events-could be discharged earlier in the health care environment of Austria.All early complications requiring immediate attention, such as postoperative hemorrhage or infarcts, occurred within 4 days after surgery.All late complications seen after discharge were readily identified in the outpatient setting, and were associated primarily with wound complications and infections.
Furthermore, to decrease the LOS among neurosurgical patients in Austria, special attention must be paid to patients after transphenoidal pituitary surgery, given that a substantial number of events associated with hyponatremia may potentially be life-threatening.Similarly, diminished levels of potassium in patients with a cardiac comorbidity should be normalized before admission.Steroid use in patients admitted for brain tumor surgery should be critically assessed for reduction or termination, if possible, given that unnecessary steroid prescription is associated with an increased complication rate and extended hospital stay [37][38][39][40].
In addition, a concomitant decrease in preventable unplanned readmission, thus avoiding unnecessary costs, can be accomplished only if the risk factors for readmission have been identified.Herein, we identified that a preoperative sodium level < 135 mm/L, prior deep vein thrombosis, the presence of psychosis, and transfer from another department or hospital were independent risk factors for unplanned readmission among neurosurgical patients.With regard to unplanned reoperation, we performed a detailed analysis and identified that age �90 years, urgent or emergent index operation, extended LOS, and transfer to a rehabilitation center after index hospitalization, among other factors, were statistically associated with unplanned reoperation.
All the above-identified factors must be considered when regulatory measures to decrease the LOS in neurosurgery are developed in health care policies.In Austria, increased resource allocation for outpatient care would be necessary to provide a safe environment for neurosurgical patients when the LOS is further decreased [38].Similarly, for optimization of preoperative outpatient care, we identified a preoperative in-hospital event rate of 1.1%.Most in-hospital adverse events occurring before the index surgery were associated with infection.Our results emphasize that patients are at risk of complications even before they undergo surgery; therefore unnecessary inpatient days before surgery, as well as surgical delays after hospital admission, should be avoided.We also identified that several abnormalities in preoperative laboratory values were associated with preoperative events.These findings suggest that patients who are predisposed to complications could be identified, and their clinical condition could be optimized before hospital admission for an elective neurosurgical operation.
Finally, our study provides a definition of postoperative events that could be used for future comparative analyses of neurosurgical patient populations, by defining a postoperative adverse events as any abnormal or unexpected neurosurgical event occurring within 90 days after the index surgery, and contributing to a prolonged hospitalization, readmission, or reoperation [7,[41][42][43][44].In our cohort, the proportion of patients who experienced a postoperative event, according to this definition, was 8.4% (n = 96).

Strengths and limitations
The major limitation of our study is its single-center design, which limits the generalizability of our results to other centers in Austria.Although a comparison with the three other large academic centers in Austria might have increased the reliability of the findings, given that patients with the most complex cases requiring comprehensive care are often referred to those centers, the selection bias toward less complex surgeries in the five regional hospitals might have been too pronounced to enable a detailed analysis.However, by taking the unspecific measure of the LOS into account, clear parallels can be seen, thereby allowing for an indirect extrapolation [35].Furthermore, because Austria is a small country with no more than 9 million inhabitants, any major differences in patient care across the nine neurosurgical centers, which could potentially have greatly influenced the outcome parameters analyzed herein, would be expected to be small, but nonetheless must be critically addressed.Furthermore, the study period's spanning January through December of 2020, in the midst of the COVID-19 pandemic, must be critically considered.In contrast to many other neurosurgical departments worldwide, patient care at our institution was not affected by the COVID-19 pandemic to an extent that could have made our study population not representative in this specific regard [45].Among the multifactorial reasons for the lack of influence of the pandemic at our institution, the most important reason was that our neurosurgical department is situated in a separate building from the main hospital, where all the other departments are located.Therefore, neither the neurosurgical ICU nor our general ward's bed capacity was affected by any restrictions during the study period.Indeed, the overall case load was slightly greater than that in previous years, thus indicating that the any limitations due to the study period itself might have been counterintuitively small.Simultaneously, our analysis encompassed the entire spectrum of neurosurgical diseases and procedures across all age groups.Furthermore, because our analyses were not based solely on administrative datasets with coded information, we were able to collect extensive and precise information on patient characteristics, perioperative factors, and outcomes.Nonetheless, the descriptions of intraoperative events in this study were restricted to the reports of the operating surgeons.

Conclusion
This study identified risk factors for prolonged LOS, readmission, and reoperation in a diverse neurosurgical patient cohort in Europe.The findings highlight LOS among neurosurgical patients in Austria could feasibly be decreased if outpatient care were tailored to the specific needs of this vulnerable patient population.